1. Field
The present invention relates to tape storage media and more particularly, to utilizing tape storage media segmentation to improve data access performance in a tape storage system.
2. Description of the Related Art
With each new generation of tape storage technology, the capacity of available tape storage medium increases. The total storage capacity of a tape depends on many factors, including the physical dimensions of the tape, the data compression, if any, used to write data to the tape, the number of tracks across the width of the tape, and so forth. Another factor that may distinguish physical capacity from usable capacity is that the usable capacity is often defined to be slightly less than the physical capacity. This is due, in part, to servo tracks, data block headers, and other metadata blocks throughout the tape.
As total tape storage capacity increases, however, so too does the time required to access data on a tape. For many data storage uses, such as a data backup, longer access time to the data is acceptable. However, many other data storage applications would benefit from faster data access times even though tapes of greater capacity and increased data access times are used in the storage system.
For tape storage applications, data is typically stored onto a magnetic tape medium, such as a metallic ribbon, within a tape cartridge using a tape drive. The tape medium conventionally is designed to include a plurality of tracks that are distributed across the physical width of the tape medium and run the physical length of the tape medium. A tape write head within the tape drive is typically capable of writing up to sixteen tracks at one time, starting at one end of the tape and moving along the length of the tape. When the tape write head reaches the end of the tape, the head is aligned over the proximate track set, the direction of the tape is reversed, and the write head writes an additional sixteen tracks in the opposite direction. This “serpentine” pattern may continue until all tracks have been written.
The process for reading data from the tape medium is essentially the same. A tape read head moves across the tape medium and reads sixteen tracks from one end of the tape medium to the other. The tape read head then realigns to read an additional sixteen tracks and moves over the second set of tracks in the opposite direction.
Given the large capacity of conventional tape storage devices, various data blocks may be stored on a single tape medium. The location of each of these data blocks may be marked on the tape using block header information, data pads (areas of tape where data is intentionally not written), and other conventional identification means and methods. The tape read head is able to locate a particular block of data by using one or more servo tracks that are written onto the tape storage medium.
More recently, manufacturers of tape storage products have directed their attention in part to improving data access time using tape storage drives and cartridges. One method that has been employed to address the problem of increased data access time is to employ various levels of transparent buffering in which tape data may be stored in connection with other storage mediums, such as a direct access storage device (DASD) or an optical disk. If the requested tape data is stored on a DASD cache, data retrieval time may be improved greatly. However, the storage capacity of a DASD cache is typically significantly less than that of a tape storage system, and the DASD cache must migrate much of the data to tape cartridges in order to be able to buffer more recent data. For this reason, a DASD cache only improves data retrieval time for data that is in the DASD cache at the time of the data request, but does not improve the time for much of the data that has been migrated to tape and demoted from the cache.
In the case of storing data on an optical disk, data access times may be improved over that of a tape, but typically the storage capacity of an optical disk is much less than that of a tape cartridge. Currently, technology allows as much as 300 Gb of non-compacted data to be stored on a single, standard tape cartridge.
Another method of improving data access time is to segment the tape storage medium into two or more segments and to write data to the segments in a sequential manner. A tape segment may include a specified capacity, or physical length of tape, that is less than the total capacity of the tape. For example, a tape storage medium may be divided into two segments. When writing data to the tape, the data is written to the first segment and then to the second segment. This method improves data access time in that the first segment may be written to or read from without physically forwarding all the way to the end of the tape storage medium.
The first segment may include, for example, only one fifth of the total tape storage capacity, and data access time is greatly improved when the first segment is located at the physical beginning of the tape. In this way, the tape drive need only advance one fifth of the way through the total length of the tape medium, rather than all the way to the physical end of the tape, before reversing direction. The data stored in the capacity of the first segment is located near the beginning of the tape, rather than being distributed along the entire length of the tape improving data access time. The data stored in subsequent segments is distributed further from the beginning of the tape which increases the data access time.
What is needed is a process, apparatus, and system for improving data access performance of a tape storage system using tape media segmentation. Beneficially, such a process, apparatus, and system would allow a user to take advantage of the tape media segmentation in order to quickly access specified data.